4.2. Identifying and mapping high SLR risk areas
4.2.2. CVI Analysis
Figure 5 illustrates highly vulnerable areas along the EM coastline in the Umhlanga area. Built up areas situated within the coastline and 100m HWM (setback line) outlined in purple are the most vulnerable to SLR impacts. For the purpose of this study, the CVI maps concentrate on specific sections of the coast as it is too extensive to cover the entire coastline. Other areas vulnerable to future SLR impacts include:
Northern region - Westbrook, Umdloti, Virginia, Durban North Central region - central Durban region, Blue Lagoon, Durban Port
Southern region - Bluff (Glenardle), Isipingo Beach, Amanzimtoti, Kingsburgh, Umkomaas, Clansthal.
However, there are no residential properties located within the central Durban region. The other maps covering the rest of the coastline are presented in the separate pdf file as Appendix B.
Figure 5: A continuum of map segments showing development and natural vegetation exposed to SLR impacts under the 100HWM in Umhlanga
Estimations from the CVI are not a complete indication of vulnerability, however they do deliver a comparative index (Palmer et al. 2011). In the past, the KZN coast has undergone significant erosion damage, and it is anticipated that these events will become more frequent. It is projected that the coastline will experience erosion events again and that the CVI locations ranked as “high” will be at greatest risk. Properties within 100m of the HWM and situated in neighbouring areas of exceptionally high CVI scores may potentially be at risk (Palmer et al. 2011). The nearness of these properties to the HWM is important to determining the level of comparative risk, with developments, including infrastructure, that are within 2m (vertical distance) of the HWM more probable to be impacted by SLR impacts and associated extreme weather events than structures further inland (Palmer et al. 2011).
Friedrich and Kretzinger (2012), for instance, conducted a study of the vulnerability of the wastewater infrastructure, both collection and disposal such as pipelines and manholes, pumping stations and wastewater treatment plants, to SLR in EM. The study found that regions at Amanzimtoti South and Isipingo Beach along with two regions of the CBD, namely the east and west regions and Maydon Wharf contained the most vulnerable manholes and pipelines. Based on the CVI analysis, there are no manholes in these areas that are within the high-risk zone but there are manholes found in Newsel Beach and Umhlanga where they are most vulnerable. Similarly, there are no pipelines in these areas that are
within the high-risk zone. According to the CVI, Umhlanga, south of the Durban Harbour entrance (i.e., the whaling station), near Mlazi River mouth and Newsel Beach have sewer pipelines that are highly vulnerable. The Point Road pumping station is highly vulnerable because of its size, connectivity and underground parts. The CVI Analysis also indicates that this pumping station is in the high-risk zone, as well as a few more pumping stations located between the South and North Beach coastal strip. The wastewater treatment plant that is most vulnerable is the Central Wastewater Treatment Plant (WWTP) owing to its geographic location and sensitivity in the past. The CVI analysis also shows that the central sewer systems area is highly vulnerable, however the north and south also have sewer systems areas within the high-risk zone, particularly near the river mouth of most rivers along the coast. The researchers advised that these components have to be monitored, particularly for rises of influx, and ought to be prioritised for adaptive actions. In addition to the CVI analysis, the Umhlanga pier at McCausland Crescent, the pier at Sometseu Road Outfall, the Bay of Plenty pier at Patterson Groyne North and the North Beach pier at Patterson Groyne South, located along the EM coastline between 31o 5’ 21’’ E; 29o 43’ 36’’ S and from 31o 2’ 14’’ E; 29o 50’ 41’’ S to 31o 2’ 20’’ E; 29o 51’ 1’’ S are the most vulnerable as they are within the high-risk zone.
In addition, the wastewater infrastructure in EM will be capable to manage the early phases of SLR (i.e., when the water table along the coast is projected to increase, causing an enhanced entry and waterflows into pipes, pumping stations and wastewater treatment plants) as a result of the current, vacant facility in the most impacted pumping stations and wastewater treatment plants (Friedrich and Kretzinger 2012). Such a design provides resilience to the system, and is a great insurance policy in the instance of a few expected SLR impacts for the EM. During this time, the infrastructure may reach the end of its projected lifespan, which will require either refurbishment or provide the opportunity to move the infrastructure to a less vulnerable location.
Vulnerable zones can be recognised for future risk management (Palmer et al. 2011). Existing developments located close to the shore are at higher risk of being destroyed. Therefore, options of defend and retreat ought to be investigated. However, in urban zones where there is probably not much space for retreat/relocation or adaption under projected SLR scenarios, options may be more complicated. Consequently, management mediations need to be carefully planned using Coastal and Shoreline Management Plans (Palmer et al. 2011). Furthermore, new development should be setback sufficiently giving the coastline space to move up the shore as SLR is experienced. Alternatively, when developing new sites, one should consider doing so away from risk prone areas. Portions of the KZN coastline are vulnerable to coastal erosion, therefore public and financially critical infrastructure may be impacted if it is in very near proximity to the HWM. Current and future management decisions need to ascertain the most suitable management options, dependent upon the nature, value, life expectancy, and impacts of possible loss of developments.
The use of the CVI alone will not provide a conclusive understanding of development and/or properties lying within the projected 300mm SLR curve or the 100m setback from the HWM. Therefore, this study assessed SLR impacts on areas demarcated only between the 100m HWM and the predicted 300mm SLR, and thus will be more precise when analysing potential areas vulnerable to SLR.
4.3. Risk assessment of SLR impacts on coastal ecosystems (dunes and forests)